user.md

User Guide

Topic Based System

The topic_based system implements hardware_interface::SystemInterface supporting command and state interfaces through ROS topic communication layer.

MoveIt and Isaac sim integration

Follow the instructions in the MoveIt and Isaac sim integration guide to setup your robot for MoveIt and Isaac sim integration.

ros2_control urdf tag

The topic_based system interface has a few ros2_control urdf tags to customize its behavior.

Parameters

• joint_commands_topic: (default: "/robot_joint_command"). Example: <param name="joint_commands_topic">/my_topic_joint_commands</param>.
• joint_states_topic: (default: "/robot_joint_states"). Example: <param name="joint_states_topic">/my_topic_joint_states</param>.
• trigger_joint_command_threshold: (default: 1e-5). Used to avoid spamming the joint command topic when the difference between the current joint state and the joint command is smaller than this value, set to -1 to always send the joint command. Example: <param name="trigger_joint_command_threshold">0.001</param>.
• sum_wrapped_joint_states: (default: "false"). Used to track the total rotation for joint states the values reported on the joint_commands_topic wrap from 2pi to -2pi when rotating in the positive direction. (Isaac Sim only reports joint states from 2pi to -2pi) Example: <param name="sum_wrapped_joint_states">true</param>.

Per-joint Parameters

• mimic: Defined name of the joint to mimic. This is often used concept with parallel grippers. Example: <param name="mimic">joint1</param>.
• multiplier: Multiplier of values for mimicking joint defined in mimic parameter. Example: <param name="multiplier">-2</param>.

Modifying the urdf ros2_control tag for new robots

If your robot description support mock_components you only need to change <plugin>mock_components/GenericSystem</plugin> to <plugin>topic_based_ros2_control/TopicBasedSystem</plugin>, make sure to add the joint_commands_topic and joint_states_topic to point to the correct topics.

        <ros2_control name="name" type="system">
            <hardware>
                <plugin>topic_based_ros2_control/TopicBasedSystem</plugin>
                <param name="joint_commands_topic">/topic_based_joint_commands</param>
                <param name="joint_states_topic">/topic_based_joint_states</param>
                <param name="sum_wrapped_joint_states">true</param>
            </hardware>
            <joint name="joint_1">
                <command_interface name="position"/>
                <state_interface name="position">
                  <param name="initial_value">0.0</param>
                </state_interface>
                <state_interface name="velocity"/>
            </joint>
            ...
            <joint name="joint_n">
                <command_interface name="position"/>
                <state_interface name="position">
                  <param name="initial_value">0.0</param>
                </state_interface>
                <state_interface name="velocity"/>
            </joint>
            ...
            <joint name="mimic_joint_1">
                <param name="mimic">joint_k</param>
                <param name="multiplier">1</param>
                <command_interface name="position" />
                <state_interface name="position">
                  <param name="initial_value">0.0</param>
                </state_interface>
                <state_interface name="velocity"/>
            </joint>
            ...
            <joint name="mimic_joint_n">
                <param name="mimic">joint_kn</param>
                <param name="multiplier">1</param>
                <command_interface name="position" />
                <state_interface name="position">
                  <param name="initial_value">0.0</param>
                </state_interface>
                <state_interface name="velocity"/>
            </joint>
        </ros2_control>